Sand mold containing a chill section and method of treating same



United States Patent O SAND MOLD CONTAINING A CHILL SECTION AND METHOD OF TREATING SAME Paul I. Nelf, Lansing, 111., assignor to American Steer Foundries, Chicago, 111., a corporation of New Jersey No Drawing. Application December 12, 1955, Serial No. 552,658

7 Claims. (Cl. 22- 214) This invention relates to metal founding and more particularly to a coating or wash for a chill section in a mold used to produce chilled steel castings.

The invention comprehends a method of and compotion for coating a chill section in a mold. It is well known to those familiar with the art of metal founding that a cast iron or cast steel object may be formed with all or part of its outer surface hardened by means of a chilling process. This is usually done by embedding in the mold a metal or graphite chill which, when on contact with the surface of the cast metal, conducts the heat therefrom more rapidly than the refractory surfaces of the mold and thus produces a harder surface on the chilled portion of the casting.

It is essential that the surface of a chill, like all other surfaces of a mold cavity, be coated with a wash of some type in order to facilitate separation of the cast article from the mold upon removal of the casting. The type of coating needed for the chill section of a mold is different from that needed for the refractory section of a mold and the physical characteristics of the materials involved are not alike.

Although several compositions have been successfully employed as chill Washes in the casting of iron, the lack of success with any known cast iron chill wash has heretofore rendered more diflicult the successful casting of steel.

One important reason that conventional chill washes have been unsuccessful has been their failure to provide a proper barrier or layer of insulation between the hardened steel and the chill. Certain washes permit relatively large gas or vapor bubbles to form between the steel casting and the chill, with the result that frequent cracks and structural failures occur in the castings. Also none of the washes have completely prevented eroded refractory material from other portions of the mold from entering between the surfaces of the casting and the chill with the result that the refractory inclusions in the chilled surface render it rough and uneven.

It is, therefore, a primary object of this invention to provide a method of coating a chill section of a mold particularly adapted for use in casting steel.

It is another object of the invention to provide a chill wash composition particularly adapted for steel castings.

Another object of the invention is the provision of a chill wash capable of forming a relatively thin uniform layer of gas or vapor between a chill and a steel casting in a mold.

A further object of the invention is the provision of a chill wash capable of preventing refractory material from entering between a chill surface and a steel casting in a mold.

Yet another object of the invention is the provision of a chill wash that is economical and may be readily applied by either brushing or spraying.

Still another object of the invention is to provide a purely organic chill wash free of any refractory constituents.

A more specific object of the invention is the provision of a chill wash comprising a resin in an alcohol solvent.

These and other objects of the invention will be apparent from an examination of the following description and claims.

After much research into the problem of chili washes for steel castings, I have discovered that although the gas bubbles which often form between the surfaces of a chill and the casting in a mold cause imperfections and therefore are undesirable, a relatively thin uniform barrier, or film, or vapor or gas formed between the surfaces of the chill and casting results in the production of a casting having smooth, even outer chilled surfaces and is highly desirable.

I have found a way to successfully produce a chilled cast steel object by controlling the formation of a relatively thin, uniform gas or vapor barrier in the mold between the chill and the casting. I have done this by coating the chill section of the mold with a relatively thin film of a new mold wash which has not been used heretofore in the founding art. The composition of my chill wash is a resin material taken from the class of resins consisting of polyvinyl acetate and methyl methacrylate.

In order to apply a relatively thin uniform coating, or film, of the composition to the chill section of a mold, the resin is first dissolved in a suflicient quantity of an appropriate solvent such as methyl alcohol in the case of polyvinyl acetate and acetone in the case of methyl methacrylate, to produce a liquid of a consistency de sirable for either spraying or brushing the solution on the chill.

Upon application of a relatively thin coat of the liquid solution, the coated surface is permitted to dry. The total evaporation of the solvent leaves the residual resin in a uniform layer or film on the surface of the chill.

When the cast steel is poured into the mold the residual resin film upon being subject to the intense heat of the mold steel forms a relatively thin uniform vapor barrier between the sides of the chill and the steel casting with the result that the chilled surface produced on the steel casting is smooth and uniform, and entirely free from defects or failures due to gas bubbles or refractory inclusions forming in the cast metal.

It will be understood, of course, that this composition may be applied to the entire surface of a mold formed completely of metal and/or graphite where it is desired to chill the entire surface of the steel casting.

I claim:

1. A method of treating, for casting steel and the like, a sand mold having a chill section embedded in the sand thereof of relatively high heat conductivity, comprising coating the chill section only thereof with a nonaqueous solution including a material from the group comprising polyvinyl acetate and methyl methacrylate dissolved in an appropriate solvent, in a thin film and permitting the solvent to evaporate leaving a uniform coating of the material on the surface of the chill section.

2. A method of treating, for casting steel and the like, a sand mold having a chill section embedded in the sand thereof of relatively high head conductivity, comprising coating the chill section only thereof with a nonaqueous solution of the group including polyvinyl acetate dissolved in methyl alcohol and methyl methacrylate dissolved in acetone, in a thin film and permitting the solvent to evaporate leaving a uniform coating of the material on the surface of the chill section.

3. A method of treating, for casting steel and the like, a sand mold having a chill section embedded in the sand thereof of relatively high heat conductivity, comprising coating the chill section only thereof with a nonaqueous solution consisting solely of one of the group polyvinyl acetate dissolved in methyl alcohol and methyl methac.

rylate dissolved in acetone, in a thin film and permitting the solvent to evaporate leaving a "uniform "coating of the material on the surface of the chill section.

4. Amethod of treating, for-casting steel and the like, a sand mold having a chillsection embedded inthe sand thereof of relatively high heat conductivity, comprising coating the chill section only thereof with a fionaqueous solution including polyvinyl acetate dissolved in methyl alcohol, in a thin film and permitting the solvent to evaporate leaving a uniform coating of the material on the surface of the-chill section.

5. A method oftreating, for casting steel and the like, asand mold havingla chill section embedded in the sand thereof of relatively high heat conductivity, comprising coating the chill section only thereof with a nonaqneons solution including methyl methacrylate dissolved in acetone, in a thin film and permitting the solvent to evaporate leaving a uniform coating of the material on the surface of the chill section.

6 A sand mold for casting steel and the like having a chill section embedded in the sand thereof of relatively high heat conductivity, and a thin film of material on the chill section only, selected from the group dry polyvinyl acetate and methyl methacrylate.

4 7. A sand mold for casting steel and the like having a chill section embedded in the-sam'd 'thereof'of' relatively high heat conductivity, and a thin film of material on the chill section only, selected from the group polyvinyl acetate and methyl methacrylate, and containing only such material.

References-Cited in the :file of this patent UNITED STATES PATENTS OTHER REFERENCES Wakernan: The Chemistry ofCommerei'al Plastics, pages 317 and 480. Reinhold Publishing -Corp-., 330 West 42nd St., N. 

1. A METHOD OF TREATING, FOR CASTING STEEL AND THE LIKE, A SAND MOLD HAVING A CHILL SECTION EMBEDDED IN THE SAND THEREOF OF RELATIVELY HIGH HEAT CONDUCTIVITY, COMPRISING COATING THE CHILL SECTION ONLY THEREOF WITH A NONAQUEOUS SOLUTION INCLUDING A MATERIAL FROM THE GROUP COMPRISING POLYVINYL ACETATE AND METHYL METHACRYLATE DISSOLVED IN AN APPROPRIATE SOLVENT, IN A THIN FILM AND PERMITTING THE SOLVENT TO EVAPORATE LEAVING A UNIFORM COATING OF THE MATERIAL ON THE SURFACE OF THE CHILL SECTION. 